Authors: Randy Vines, Extension Specialist, Biotechnology Information; Virginia Tech
Publication Number 443-002, March 2002
The goal of plant breeding is to combine desirable traits from different varieties of plants to produce plants of superior quality. This approach to improving crop production has been very successful over the years. For example, it would be beneficial to cross a tomato plant that bears sweeter fruit with one that exhibits increased disease resistance. To do this, it takes many years of crossing and backcrossing generations of plants to obtain the desired trait. Along the way, undesirable traits may be manifested in the plants because there is no way to select for one trait without affecting others. Another limitation of traditional plant selection is that breeding is restricted to plants that can sexually mate.
Advances in scientific discovery and laboratory techniques during the last half of the twentieth century led to the ability to manipulate the deoxyribonucleic acid (DNA) of organisms, which accelerated the process of plant improvement through the use of biotechnology.
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Genes are found within the genome and serve as the "words" of the instruction manual. When a cell reads a word, or in scientific terms "expresses a gene," a specific protein is produced. Proteins give an individual cell, and therefore the plant, its form and function. Genes (words) are written using the four-letter alphabet A, C, G, T. The letters are abbreviations for four chemicals called bases, which together make up DNA. DNA is universal in nature, meaning that the four chemical bases of DNA are the same in all living organisms. Consequently, a gene from one organism can function in any other organism.
The ability to move genes into plants from other organisms, thereby producing new proteins in the plant, has resulted in significant achievements in plant biotechnology that were not possible using traditional breeding practices.
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Nature's way
One method to transfer DNA into plants takes advantage of a system found in nature. The bacterium that causes "crown gall tumors" injects its DNA into a plant genome, forcing the plant to create a suitable environment for the bacterium to live. After discovering this process, scientists were able to "disarm" the bacterium, put new genes into it, and use the bacterium to harmlessly insert the desired genes into the plant genome.
Cellular target practice
In the "biolistic" or "gene gun" method, microscopic gold beads are coated with the gene of interest and shot into the plant cell with a burst of helium. Once inside the cell, the gene comes off the bead and integrates into the cell's genome.
That's shocking!
It was also discovered that plant cells could be "electroporated" or mixed with a gene and "shocked" with a pulse of electricity, causing holes to form in the cell through which the DNA could flow. The cell is subsequently able to repair the holes and the gene becomes a part of the plant genome.
Selecting the right cells
When using these methods, new genes are successfully introduced into only a small percentage of the cells, so scientists must be able to "pick out" or "select" the transformed cells before proceeding. This is often done by concurrently introducing an additional gene into the cell that will make it resistant to an antibiotic. A cell that survives antibiotic treatment will most likely have received the gene of interest as well; that cell is subsequently used to propagate the new plant. There is a concern that the gene giving antibiotic resistance could naturally be transferred to bacteria once the transgenic plant is in the wild, making bacteria resistant to antibiotics that are used to fight human infection. Scientists are currently devising ways to select for transformed cells that will alleviate this issue.
Timeline of Plant Biotechnology
1700s -- Naturalists identify hybrid plants
1860s -- Austrian botanist and monk Gregor Mendel studies pea plants and recognizes that specific traits are passed from parents to offspring - these traits are eventually discovered to be genes
1900 -- European botanists begin to improve plant productivity using genetic theories based on Mendel's work
1922 -- Farmers purchase hybrid seed corn created by crossbreeding two corn varieties
1953 -- Structure of DNA is discovered - marking the beginning of modern genetic research
1970s -- Hybrid seeds are introduced to developing countries to increase food supplies
1973 -- Genetic engineering is used to precisely manipulate bacterial DNA
1983 -- First GM plant is created; a tobacco plant resistant to an antibiotic
1985 -- GM plants resistant to viruses, bacteria, and insects are field tested
1986 -- EPA approves the release of the first GM crop (herbicide resistant tobacco)
1990 -- First successful field trial of GM cotton (herbicide resistant)
1992 -- FDA decides GM foods will be regulated as conventional foods
1994 -- FlavrSavr Tomato becomes the first GM food to be approved for sale
1995 -- Herbicide resistant canola, corn,
2000 -- cotton, soybeans, sugar beet as well as insect or virus resistant corn, cotton, papaya, potato, squash, tomato approved in the U.S.
2001 -- "Golden rice" which may help prevent millions of cases of blindness and death caused by Vitamin A and iron deficiencies undergoes continued testing
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Input traits
An "input" trait helps producers by lowering the cost of production, improving crop yields, and reducing the level of chemicals required for the control of insects, diseases, and weeds.
Input traits that are commercially available or being tested in plants:
(credit: Agricultural Research Service, USDA)
Output Traits
An "output" trait helps consumers by enhancing the quality of the food and fiber products they use.
Output traits that consumers may one day be able to take advantage of:
"Value-added" traits
Genes are being placed into plants that completely change the way they are used.
Plants may be used as "manufacturing facilities" to inexpensively produce large quantities of materials including:
Plants are being produced with entirely new functions that enable them to do things such as:
Canola Plants made Resistant to High Concentrations of Salt Through Biotechnology
(credit: Dr. Eduardo Blumwald, University of California, Davis)
Canola plants grown in the presence of a high concentration of salt. Non-genetically modified canola (non-GM) or canola genetically modified to have high, medium, or low tolerance to salt.
Plants with "input traits" that are commercially available include:
Plants may become available with "output traits" including:
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Some of the potential benefits from using transgenic plants include:
Potential risks associated with transgenic plants include:
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GM foods require labeling only if they differ significantly in safety, composition, or nutritional content when compared to their non-GM counterparts. Additionally, the FDA requires a GM food to be labeled if it contains a known allergen unless data have shown that there is no allergy risk.
In Organic products
Organic standards reflect a "zero tolerance" policy concerning transgenic products and organisms. Organic food producers are taking precautions to minimize the risk of unintentional contamination of their products with transgenic ones.
In Canada
The Canadian Food Inspection Agency, Health Canada, and Environment Canada strictly regulate agricultural biotechnology products. They currently require GM foods to be labeled if they differ significantly in composition or nutritional value and support a voluntary labeling policy for others.
In Europe
The acceptance of GM crops by the European Union has been more reserved. However, recent statements made by European Union officials suggest that their position may be changing as they are calling for their policies regarding GM crops to be based on scientific principles rather than on public opinion and misconceptions. Europe currently favors labeling of all GM foods and a system that would allow for "identity preserved" processing in which foods would be guaranteed to contain no genetically modified products.
(credit: USDA National Agricultural Statistics Service, Pew Initiative on Food and Biotechnology)
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